This invention relates to an electric circuit with safety switches, and more particularly to such an electric circuit for use in an apparatus of the type, in which there are provided safety switches in the respective portions thereof, for example such as a door of the apparatus, so that abnormal conditions, such as an open door, may be detected by means of the aforesaid safety switches, thereby interrupting an electrically conductive path between at least one of a plurality of loads in the apparatus and the main electric power source.
FIG. 1 shows such a prior art electric circuit with safety switches of the type described. As shown, safety switches S1, S2 . . . Sn, which are provided in suitable positions and components of the apparatus, are connected with main electric power source E through main switch Sm in series with load Z of the apparatus. The contacts associated with safety switches S1 . . . Sn are opened in the event of an abnormal condition in a reproducing apparatus, for example, thereby interrupting the electrical conductive paths between load Z and main electric power source E.
However, since the aforesaid prior art electric circuit includes a plurality of safety switches connected in series in a circuit which connects the main electric power source with a load, the safety switches are actuated at the same voltage as that of the main electric power source, and also with the same current which is being provided to the apparatus. As a result, if the apparatus requires a high operating voltage, and/or consumes a great amount of current, the respective safety switches must withstand and meet the electrical requirements accruing from the use of apparatus of such a large capacity. This in turn requires increased capacity of the safety switches, with their resulting low efficient operation. More specifically, for example, the increased size of the safety switches requires a considerably higher external force for switching the contacts of the safety switches. Thus, in case such safety switches are provided for detecting the open or closed position of a door in an apparatus, there is the disadvantage that a commensurately greater force is required for opening and closing the door. If safety switches having large electrical capacity are used to conduct a high voltage or high current, there results the well-known switching contact discharging phenomenon, whereby the switch contacts are damaged, which impairs the service life, durability and reliability of the safety switches themselves. Additionally, there is another shortcoming of prior art apparatus of the type specified herein and that occurs in apparatus requiring a high voltage from a main electric power source, which in turn requires high voltage conductors for the connection of the respective safety switches therein. This causes many safety problems. This is particularly true where high voltage conductors are connected to a door of the apparatus, such that the safety switch associated therewith to detect the open or closed condition thereof, itself causes a dangerous condition. More particularly, as shown in FIG. 1, when the contacts of safety switch S2 are opened, load Z will be disconnected from main electric power source E, although the portion of the circuitry from main power source to safety switch S2 remains energized at a high voltage. Accordingly, it would be particularly dangerous to check the interior of an apparatus with such a door of the apparatus, for example, kept open.